The present invention relates to a method for determining diagnostically significant component in a given test mixture. More particularly, the present invention relates to a method useful in determining thyroid gland activity.
There are numerous instances in which it is desired to separate and/or determine the amount of a particular component in a test sample containing the desired component and additional materials. Of particular interest in this regard are the testing of biological products derived from animal and plant sources. In one aspect, directed at the testing of such biological products, it may be desired to separate and/or determine a given endogenous component present in the product. For example, numerous procedures and techniques are known for the determination, in human sera of hormones, enzymes, antigens, various protein moieties, vitamins, etc., which can be produced in the body. In still another aspect related to the testing of biological products, it is often times important to ascertain the level of an exogenous material as, for example, in the case of humans, materials such as poisons, narcotics, medications, etc., which are introduced into the body orally or intravenously. While in many cases the diagnostic tests involving both endogenous and exogenous components can be conducted directly on the test fluid without prior isolation or separation of the component, more frequently it is necessary that the diagnostically significant component be, at least partially, separated or isolated from the test mixture.
A prime example of a diagnostic test in which separation of the diagnostically significant component from the sample is necessary is found in the methods employed to test thyroid gland function. Currently, two of the most widely used methods employed in the testing of thyroid gland activity are the tests commonly referred to as the T-3 and T-4 tests. The former measures the unsaturated binding capacity of thyroid hormone binding globulin and other proteins in the body fluid, e.g. blood, while the latter measures the total quantity of the hormone thyroxine within a sample of serum, e.g. blood. The T-4 test measures the level of thyroxine (C.sub.15 H.sub.11 I.sub.4 NO.sub.4), while the T-3 test measures the unsaturated thyroid hormone protein binding capacity for T-4. Both methods employ the use of radioisotope labeled hormones as tracers. In both the T-3 and T-4 methods,the tracer hormone is admixed with a test serum from the body which contains the thyroid hormones thyroxine (C.sub.15 H.sub.11 I.sub.4 NO.sub.4), T-4, and triiodothyronine (C.sub.15 H.sub.12 I.sub.3 NO.sub.4), T-3, and the thyroid hormone binding proteins. By radioassaying either the free or the bound hormone, the amount of endogenous hormone which is bound to the thyroid binding hormone proteins within the serum can then be determined.
The accuracy of the T-3 and T-4 tests depends on the effective separation of the free and bound thyroid hormone in the test procedure. U.S. Pat. No. 3,666,854 and 3,776,698 disclose thyroid hormone test procedures in which the desired separation is accomplished by the use of a solid, particulate, inorganic crystalline material which is added to the test fluid, and on which the free or unbound hormones are selectively adsorbed. The T-3 and T-4 tests set forth in those patents, in general, require a relatively large amount of the particulate solid sorbent. Furthermore, to obtain accurate results relatively close control of the solid particle size is necessary. Moreover, in the case of the T-4 test, in order to ensure adsorption of the unbound or free thyroxine on the particulate solid sorbent, it is generally necessary to have an incubation time of approximately 30 minutes, making the test time consuming. It should further be noted that the above described T-3and T-4 tests, requiring the addition of a solid particulate sorbent to the test solution, pose greater manipulation problems in the laboratory than procedures involving primarily the use of liquids, which can be accurately and easily metered by commonly available laboratory apparatus.